The interrelationship between the effects of insulin-like growth factor I and somatostatin on growth hormone secretion by normal rat pituitary cells: the role of glucocorticoids

Endocrinology
S W LambertsL J Hofland

Abstract

Both insulin-like growth factor I (IGF-I) and somatostatin (SRIH) have been shown to directly inhibit GH release and the total GH content of cultured pituitary cells. In the present study we evaluated the interrelationship between the effects of a recombinant human IGF-I analog ([Thr59]IGF-I) and SRIH on GH release by cultured normal rat pituitary cells together with the effects of glucocorticoids. In all experiments anterior pituitary cells were preincubated for 24 h without or with IGF-I, SRIH, and/or dexamethasone. Thereafter, 24-h incubations without or with IGF-I, dexamethasone, SRIH, and GHRH were performed. Both IGF-I and SRIH inhibited basal and GHRH-stimulated GH release in a dose-dependent manner; the maximal inhibitory concentrations were 5 nM IGF-I and 10 nM SRIH. These concentrations inhibited basal and GHRH-stimulated GH release by 23% and 40% (IGF-I) and 80% and 85% (SRIH), respectively. The combination of IGF-I and low concentrations of SRIH exerted an additive inhibitory effect on GHRH-stimulated GH release; IGF-I (1 nM) and SRIH (10 pM) together inhibited GH release by 50%, while the maximal inhibitory concentrations of 5 nM IGF-I and 10 nM SRIH virtually completely inhibited GH release (by 93%). Preincubation...Continue Reading

Citations

Jan 1, 1994·Life Sciences·J H Thakore, T G Dinan
Jan 1, 1996·Pharmacology & Therapeutics·M K Agarwai
Jan 1, 1994·Peptides·H Houben, C Denef
Jun 12, 2001·Comparative Biochemistry and Physiology. Part B, Biochemistry & Molecular Biology·S FruchtmanR Borski
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Sep 1, 2005·Pituitary·Joost van der HoekLeo J Hofland
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Sep 1, 1990·Journal of Endocrinological Investigation·S Ezzat, S Melmed
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